1. How do you know when its time to change your oxygen
sensor I hear you ask ? ..Well there can be number of symptoms :
( a ) Car running okay when cold , but once warm idle speed becomes erratic
.
( b ) Warning light on dash lights up , reporting code 13 , 44 or 45 .
( c ) Car using twice as much petrol than normal when you are not driving
like Michael Schumacher .
You may be lucky and find its just due to poor electrical connection from
the pigtail to the wiring loom , but we all know its never that easy .

2. Most cars built after 1981 have an oxygen sensor that is usually found
on the exhaust manifold close to where exhaust becomes one pipe .Here
it has to cope with all the engine heat and is a pig to get to . Oxygen
sensors only start to work over at 300c+ , and has a generate a tiny 0.1
to 0.9 volt signal to tell the ECM what to do no wonder they need replacing
every 100k , and at $75 they are not too expensive .

3. To remove oxygen sensor ( says the book ) " separate electrical
connector , unscrew and, then replace " . What it doesn't say is
its very difficult to remove . Years of living next an screaming SBC and
having water , mud and other un-natural elements thrown at it the threads
become seized into the cast iron of the exhaust manifold .

4. Result is, it requires quite a bit of effort to remove .Most seem
to be 22mm , so if you very lucky you may be able to get a large ring
spanner on it and lean on it as if you life depended on it .If this fails
then buy a 22mm deep with at least ½ inch drive socket ( > 45
mm deep ) and attack it with a grinder until it looks like following picture
.

5. The aim is to allow the " pig tail " wire and plastic plug
to be passed through the socket and remain undamaged while you are removing
it , or placing new sensor into manifold .
Do not just cut a slot in socket or you will cause much skin to be removed
from your knuckles when you attempt to apply force and have socket slip
and split

6. Once socket is in place over oxygen sensor , find the biggest
bar you can muster to apply torque and see if you can move it . Its worth
heating up the whole show before you start by running the engine and applying
some penetrating oil over a couple of days before hand - well it may help

7. After several minutes of going red in the face and
calling out the maker of your car unpleasant names and still no joy time
to call in the big guns . Drive up to your local exhaust shop and beg
for use of there rattle gun .
Persistence usually pays off , but if all else fails a new nut and panel
can be welded into place or you can remove the whole manifold and spend
many happy hours screaming obscenities in your garage late at night .

8. Remember when you do put the new one in it only needs 30lbs pressure
to reseat , be careful not to allow pigtail wire to melt on exhaust
and a new unit should have some sort of anti-seize command on threads
to help next time !